In the conventional formation of tobacco filler rods, a relatively wide and thin or broad stream of tobacco particles of varying sizes, usually approximately 36 inches wide, first is provided, moving vertically upwardly or downwardly towards a filler rod-forming belt moving transverse to the direction of movement of the tobacco particles. This relatively wide stream usually is provided with as even as possible distribution of tobacco across its width by various means. The tobacco particles of the relatively wide stream are gathered together on the intercepting surface of the transversely-moving belt to form a narrow filler rod thereon which has generally-increasing depth across the width of the relatively wide stream in the direction of movement of the belt. Cigarettes are formed from the continuous filler rod recovered from the gathering operation usually by lateral compression of the filler rod, followed by wrapping of the compressed rod in paper to form a continuous cigarette rod, from which individual cigarettes may be cut.
In the formation of the filler rod from a falling stream of tobacco particles, to reduce the tendency of tobacco particles to be displaced longitudinally of the narrow filler rod in a direction opposite to the direction of movement of the narrow rod-forming belt during collection of the particles to form the filler rod, thereby forming knots, balls or concentrations of particles in the forming filler rod and hence introducing lack of uniformity of tobacco weight into the filler rod stream, it has become common practice to construct the gathering belt as a flat narrow belt of air-permeable and tobacco-impermeable material and to apply a gentle vacuum through the surface. This use of a gentle vacuum has been thought to grip the tobacco particles to the surface of the belt upon contact thereby diminishing the tendency of the narrow filler rod to ball up.
Close examination by high speed photography of the gathering of the falling broad stream into a narrow filler rod of tobacco particles has revealed that, while the gentle vacuum is to a certain degree effective in preventing displacement of the particles in those portions of the conveyor where the forming filler rod is relatively thin, in thicker portions considerable peaks and valleys of tobacco particles in the forming stream occur as the vacuum loses its effectiveness on the particles remote from the surface and hence control is lost of the movement of the particles from the falling stream into the filler rod moving transverse to the direction of movement of the falling stream. This problem is compounded as the speed of filler rod-forming procedure increases.
The formation of peaks and valleys in the filler rod in this way results in a filler rod having a non-uniform weight distribution of tobacco along its length. Formation of cigarettes from such a filler rod would lead either to an inconsistent product or the rejection of a large number of cigarettes which did not conform to a narrow weight range. Either result is plainly unsatisfactory.
Similar lack of weight uniformity arises when the filler rod is formed on a belt moving transverse to a relatively wide stream conveyed by an upwardly moving chute-confined air stream.
This prior art problem has lead to the feeding of excess quantities of tobacco in the relatively wide stream from which the filler rod is formed so that the resulting filler rod contains on average an excess of tobacco over that ultimately required to form the cigarette rod. This overfeeding of the rod-forming operation attempts to provide sufficient excess tobacco in the rod so that, irrespective of the variations in tobacco weight along the length of the filler rod, substantially all the filler rod length contains a quantity of tobacco in excess of that ultimately required in the cigarette rod.
The excess tobacco is trimmed from the filler rod after its formation so that the trimmed rod contains the quantity of tobacco required for feed to the wrapping procedure and has an improved uniformity of quantity of tobacco along its length as compared to a filler rod formed without overfeeding and trimming. Typically, about a 20% overfeed of tobacco is made requiring trimming and recycling of this overfed amount.
This prior art practice of overfeeding and trimming in attempting to overcome the weight uniformity problems arising from the assembly technique is objectionable from at least two standpoints. One such objection arises from the overfeeding of the filler rod assembly. With the need to increase the speed of formation of the filler rod for faster and more economic production of cigarettes, the runability of the cigarette making machine, i.e. its ability to make cigarettes on a continuous basis without breakdown, becomes a problem since it is forced to process much more tobacco than is required in the cigarettes thereby increasing the chances of the maker choking.
Another such objection arises from the trimming of large quantities of tobacco from the filler rod for recycle to the formation of the relatively wide stream. It has been found that the trimming of the tobacco filler rod decreases the "filling power" of the trimmed tobacco upon reuse. As indicated in U.S. Pat. No. 3,357,436, the "filling power" of tobacco is a measure of the ability of the tobacco to fill a cigarette tube. At a given hardness of cigarette, the less quantity of tobacco required to achieve that hardness, the greater is the filling power of that tobacco. Thus, decreasing the filling power of the tobacco by trimming leads to either less hard cigarettes or an increased tobacco requirement, the problem increasing with increased trimming.
The above-mentioned high speed photographic examination of the filler rod during its formation additionally indicated that smaller tobacco particles tend to penetrate the surface of the portions of the filler rod already formed on the conveyor belt while the larger particles tend to lie on the surface of the already-formed rod portion. From this expected observation of the different behaviour of the differently-dimensioned tobacco particles, there results, in effect, a classification of tobacco particle sizes over the cross section of the filler rod, with smaller tobacco particles tending to be located closer to the conveyor belt and larger tending to be located remote from the belt.
This classification may lead to the undesirable effects of bad ends to the cigarettes, uneven burning rates and uneven burning temperatures, with accompanying variations of smoke constituents and taste.
The prior art procedures suffer from a number of additional drawbacks to those discussed above which result in unsatisfactory cigarettes. One such additional drawback results from the manner of formation and conveying of the filler rod from its formation to the wrapping station. The filler rod typically is formed on and is conveyed on a substantially flat moving belt which runs in a channel between opposed stationary sidewalls which confine the rod laterally. There is, therefore, frictional contact between the sidewalls and the filler rod during its formation and conveying. Variations in the coefficient of friction between the tobacco and the sidewalls, resulting from variations in the tobacco and/or variations in the sidewalls themselves, for example, due to irregular tar build up, may lead to dislodgment of tobacco particles from the body of the rod or movement of tobacco paticles to different longitudinal positions in the rod, resulting in a worsened uniformity of tobacco along its length, leading to large numbers of cigarette rejects, and, under extreme conditions, the machine may become clogged, in which event, production would have to cease until the clog is removed.
Further, in conventional cigarette-making procedures, the filler rod has a relatively wide width when first formed and is manipulated to decrease its width during passage from the chute to the commencement of the wrapping procedure. This manipulation, due to the frictional contact between the constraining walls and the tobacco in the rod, may increase the side wall friction problem mentioned above.
Heretofore it has not been considered possible to form a filler rod having the width required for feed to the wrapping procedure, typically less than about 10 mm, particularly about 5 to about 10 mm, due to an increase in the control problems in the formation of the filler rod directly from the relatively wide tobacco stream with decreased width surface, especially at high speeds of formation of filler rods, typically above about 4,000 cigarettes per minute, even with the application of suction to the underside of the rod-forming belt. The control problems arise, as mentioned above, from the increasing thickness of the filler rod on the surface across the width of the relatively wide stream and the decreasing influence of suction with increasing depth. As the rod-forming surface of the belt is made thinner, the depth of tobacco in the rod on the belt increases, thereby increasing the control problem as compared with a wider rod-forming surface.
Hence, the prior art considered it necessary to form an overwide filler rod which later is compressed laterally to decrease its width to a size suitable for feed to the wrapping procedure.